1. Field of the Invention
The present invention relates to a density correction method and an image forming apparatus, and particularly to an image forming apparatus, in which a latent image is formed by scanning a light beam on an image retaining member or by causing light from an array light source to be imaged on an image retaining member, and the latent image is subjected to development and transferred to an image recording medium, and an image is formed on the image recording medium, and to a density correction method in the image forming apparatus.
2. Description of the Related Art
There have spread image forming apparatuses, for example, an image forming apparatus such as a laser printer or an electrophotographic copying machine, in which an image is formed by irradiating a light beam on a photosensitive member while scanning the light beam thereon, or an image forming apparatus in which an image is formed by causing light from a light source formed by arrangement of a plurality of light emitting elements such as an LED array, that is, a plurality of light emission points (hereinafter referred to as an xe2x80x9carray light sourcexe2x80x9d), to be imaged on a photosensitive member by using a SELFOC lens or the like. In such image forming apparatuses, when an image is formed on an image recording medium such as paper, the density of coloring materials may become ununiform (density unevenness).
It has conventionally been known that, in a light scanning apparatus in which a light beam is scanned by using a deflector such as a polygon mirror, the intensity of a light beam is changed in order to correct uneven density caused by variation in irradiation energy in a region in which the light beam is scanned.
For example, in Japanese Patent Application Laid-Open (JP-A) No. 56-74275, the technique is proposed, wherein in order to prevent the light intensity per unit area of a light beam from decreasing as an angle of incidence xcex8 of the light beam on a photosensitive material drum 300 becomes large (see FIG. 23), setting of driving current is carried out so that the output power level increases as the angle of incidence of the light beam on the photosensitive material drum 300 becomes larger (see FIGS. 24A to 24C).
In JP-A No. 60-16058, the technique has been proposed, wherein in order to prevent a change in the beam intensity on a scanning surface by variation in the reflectance caused by the change in the angle of incidence of the light beam on a light deflector (see FIG. 25), bias current I1 is changed in accordance with an angle of incidence xcexa8 on the deflector.
Further, in JP-A No. 10-297017, the technique has been proposed, wherein in order to correct variations in the amount of light of an LED array, driving current of the LED is changed based on correction data of variations in the amount of light (see FIG. 26).
Due to the variation in irradiation energy in a region in which a light beam is scanned, or the variation in the amount of light of the LED array being corrected as described above, uneven density in the direction in which a light beam is scanned, or a direction in which light emitting elements (light emission points) of the LED array are arranged (which both directions will be hereinafter generically referred to as a xe2x80x9cscanning direction of a light beamxe2x80x9d), that is, a direction perpendicular to a direction in which an image is formed on a photosensitive member or an image recording medium, is alleviated.
Uneven density in the scanning direction of a light beam on a light image recording medium, is not necessarily caused by only energy of a light beam irradiated on the photosensitive member or variation in the energy density (ununiform irradiation).
In addition to the above-described ununiform irradiation caused by a light beam, for example, ununiform charging caused by ununiformity of a corotoron or a charge roll for applying a charge to a photosensitive member (ununiformity of charging caused in the photosensitive member), variations in the amount of a toner in a development roll of a developing machine which supplies the toner to a latent image formed on the photosensitive member (variations in the density of toner), and an ununiform distance between the development roll and the photosensitive member (variations in the distance) each cause ununiform density of coloring materials at the time of forming a toner image on the photosensitive member. As a result, uneven density of coloring materials is caused on the image recording medium.
Further, even if uneven density of coloring materials occurs in the toner image formed on the photosensitive member, uneven density of coloring materials is also caused on the image recording medium due to ununiformity of charging by a transfer corotoron or a transfer roller for transferring, to a transfer printing medium (i.e., intermediate transfer material, paper, or the like), the toner image on the photosensitive member (ununiform charging caused in the transfer material) or due to ununiform nipping force (variations in the nipping force).
However, in the above-described conventional techniques, ununiform irradiation by a light beam is only corrected, and therefore, uneven density on an image recording medium with a final image formed thereon, cannot be corrected. Particularly, in a case of a full color image, there exists a problem in that if uneven density is not corrected, color hue varies and an image of high quality cannot be obtained.
The present invention has been devised in order to solve the above-described problems, and an object thereof is to provide a density correction method and an image forming apparatus, which allow reduction in the uneven density of an image in a main scan direction of a light beam, or a direction in which light emission points of an array light source are arranged.
In order to achieve the above-described object, according to a first aspect of the present invention, there is provided a density correction method in an image forming apparatus in which a planar latent image is formed by sub-scanning in which a main scanning position of a light beam is moved relatively to an image retaining member while main scanning of a light beam is being effected on the image retaining member, and the latent image is developed and transferred to an image recording medium, thereby forming an image on the image recording medium, the method comprising the step of: based on the density of an image on one of the image retaining member and the image recording medium, correcting an intensity of the light beam in an image region within a range of one main scan so as to allow correction of uniformity of the image density in the main scanning direction of the light beam.
In accordance with the first aspect of the present invention, based on the density of an image on the image retaining member or on the image recording medium, the intensity of the light beam in the image region is corrected within the range of one main scan so that ununiformity of the image density in the main scanning direction of the light beam is corrected. That is, unlike the conventional methods, the light beam is irradiated on the image retaining member while the intensity (amount of light) of the light beam is being corrected within one main scan based on the density of a formed image. Accordingly, any density unevenness caused by, not only ununiform irradiation, but also ununiformity of charging caused in the image retaining member, variations in the density of toner, variations in the distance, ununiform charging caused in the transfer material, variations in the nipping force, and the like is solved (reduced), and density unevenness in the image region can be reduced.
At this time, in accordance with a second aspect of the present invention, preferably, after the intensity of the light beam is in advance controlled automatically at a predetermined intensity level, based on the density of an image on one of the image retaining member and the image recording medium, the intensity of the light beam in the image region is corrected within a range of one main scan, and when an amount of correction in the intensity of a light beam based on the image density is changed, the intensity is changed so that one of an intensity of the light beam in a predetermined portion of the image region, and an average value of intensities of the light beams in the main scanning direction becomes substantially equal before and after the amount of correction is changed.
That is, after the intensity of the light beam has been in advance controlled automatically at the predetermined intensity level, the light beam is irradiated on the image retaining member while the intensity of the light beam is being corrected within one main scan so as to allow correction of density unevenness in the image region. When the amount of correction is changed (including a case in which a state of making no correction is changed to a state of making a correction), the intensity level is changed so that the intensity of the light beam in a predetermined portion of the image region, or an average value of the intensities of the light beam in the main scanning direction becomes substantially equal before and after the amount of correction is changed. As a result, variations in the image density in the vicinity of, for example, a central portion of the image region having the highest visibility due to the change in the amount of correction is prevented. Accordingly, any density unevenness caused by, not only uniform irradiation, but also other factors is eliminated (reduced), and when a color image is formed, ununiform color tone caused by relative density differences between colors can be prevented.
Further, in a third aspect of the present invention, there is provided a density correction method in an image forming apparatus in which a planar latent image is formed by causing light from an array light source having plural light emission points arranged therein, to be imaged in an image forming region on an image retaining member and by effecting sub-scanning in which a position at which the light is imaged, is moved relatively to the image retaining member, and the latent image is developed and transferred to an image recording medium, thereby forming an image on the image recording medium, the method comprising the step of: based on the density of an image on one of the image retaining member and the image recording medium, correcting light emission intensities of the plural light emission points in a direction in which the light emission points are arranged, so as to allow correction of uniformity of the image density in the direction in which the light emission points are arranged.
In accordance with the third aspect of the present invention, based on the density of an image on the image retaining member or the image recording medium, light emission intensities of the plural light emission points of an array light source such as an LED array, that is, intensities of output light from the light emission points are each corrected in the direction in which the light emission points are arranged (that is, in the main scanning direction) so that ununiformity of the image density in the direction in which the light emission points are arranged is corrected. In other words, a light beam is irradiated on the image retaining member while the output intensities of the light emission points are being corrected based on the density of a formed image, not based on ununiformity in the amount of light from the array light source. Accordingly, any density unevenness caused by, not only ununiformity in the amount of light, but also ununiformity of charging caused in the image retaining member, variations in the density of toner, variations in the distance, ununiform charging caused in the transfer material, variations in the nipping force, and the like is eliminated (reduced), and density unevenness in the image region can be reduced.
At this time, in a fourth aspect of the present invention, preferably, after the light emission intensities of the plural light emission points are each previously controlled automatically at a predetermined level, based on the density of an image on one of the image retaining member and the image recording medium, the respective light emission intensities of the plural light emission points in the direction in which the light emission points are arranged, are corrected, and when an amount of correction of the light emission intensities based on the image density is corrected, the intensity level is changed so that one of the light emission intensity in a predetermined portion of the image forming region, and an average value of the light emission intensities in the direction in which the light emission points are arranged, becomes substantially equal before and after the amount of correction is changed.
That is, after the light emission intensities of the plural light emission points have been each automatically controlled in advance at a predetermined intensity level, a light beam is irradiated on the image retaining member while the light emission intensities of the light emission points are being corrected so as to correct density unevenness in the direction in which the light emission points are arranged in the image region (i.e., in the main scanning direction). When the amount of correction is changed (including a case in which a state of making no correction is changed to a state of making a correction), the intensity level is changed so that the light emission intensity in a predetermined portion of the image region, or an average value of the light emission intensities in the direction in which the light emission points are arranged, becomes substantially equal before and after the amount of correction is changed. As a result, variations in the image density in the vicinity of, for example, a central portion of the image region having the highest visibility due to the change in the amount of correction is prevented. Accordingly, any density unevenness caused by, not only uniformity in the amount of light of the array light source, but also other factors is eliminated (reduced), and when a color image is formed, ununiform color tone caused by relative density differences between colors can be prevented.
Further, in a fifth aspect of the present invention, when the intensity level is changed, the amount of correction is changed if the changed intensity level exceeds a predetermined range, thereby allowing the intensity level to be held within the predetermined range.
In accordance with a sixth aspect of the present invention, there is provided an image forming apparatus in which a planar latent image is formed by sub-scanning in which a main scanning position of a light beam is moved relatively to an image retaining member while main scanning of a light beam is being effected on the image retaining member, and the latent image is developed and transferred to an image recording medium, thereby forming an image on the image recording medium, the apparatus comprising: amount-of-correction setting means for setting, based on the density of an image on one of the image retaining member and the image recording medium, an amount of correction for correcting ununiformity of the image density in the main scanning direction of the light beam; and correction means for correcting, based on the amount of correction set by the amount-of-correction setting means, an intensity of the light beam in the image region within a range of one main scan.
According to the sixth aspect of the present invention, based on the density of an image on the image retaining member or the image recording medium, an amount of correction for correcting ununiformity of the image density in the main scanning direction of the light beam is set by the amount-of-correction setting means. Based on the amount of correction, the intensity of the light beam in the image region is corrected by the correction means within a range of one main scan.
As a result, in the same manner as in the first aspect, the light beam is irradiated on the image retaining member while the intensity of the light beam (the amount of light) is being corrected within one main scan based on the density of a formed image. Accordingly, any density unevenness caused by, not only ununiform irradiation, but also ununiformity of charging caused in the image retaining member, variations in the density of toner, variations in the distance, ununiform charging caused in the transfer material, variations in the nipping force, and the like can be eliminated (reduced).
In a seventh aspect of the present invention, preferably, intensity control means for automatically controlling the intensity of the light beam at a predetermined intensity level, and intensity level changing means which, when setting of the amount of correction by the amount-of-correction setting means is changed, changes the intensity level so that one of the intensity of the light beam in a predetermined portion of the image region, and an average value of intensities of the light beam in the main scanning direction becomes substantially equal before and after the setting is changed, are further provided.
That is, the intensity of the light beam is automatically controlled at a predetermined intensity level by the intensity control means. In image forming apparatuses, generally, such automatic control for the intensity of the light beam as described above is carried out (so-called APC: Auto Power Control). When the amount of correction set by the amount-of-correction setting means is changed (including a case in which a state of making no correction is changed to a state of making a correction), the intensity level is changed by the intensity level changing means so that the intensity of the light beam in a predetermined portion of the image region, or an average value of the intensities of the light beam in the main scanning direction, becomes substantially equal before and after the amount of correction is changed. As a result, variations in the image density in the vicinity of, for example, a central portion of the image region having the highest visibility due to the change in the amount of correction is prevented. Accordingly, in the same manner as in the second aspect, any density unevenness caused by, not only uniform irradiation, but also other factors is eliminated (reduced), and when a color image is formed, ununiform color tone caused by relative density differences between colors can be prevented.
Further, according to an eighth aspect of the present invention, there is provided an image forming apparatus in which a planar latent image is formed by causing light from an array light source having plural light emission points arranged therein, to be imaged in an image forming region on an image retaining member, by effecting sub-scanning in which a position at which the light is imaged, is moved relatively to the image retaining member, and the latent image is developed and transferred to an image recording medium, thereby forming an image on the image recording medium, the apparatus comprising: amount-of-correction setting means for setting, based on the density of an image on one of the image retaining member and the image recording medium, an amount of correction for allowing correction of ununiformity of the image density in the direction in which the light emission points are arranged; and correction means for correcting, based on the amount of correction set by the amount-of-correction setting means, light emission intensities of the plural light emission points in the direction in which the light emission points are arranged.
In accordance with the eighth aspect of the present invention, based on the density of an image on the image retaining member or the image recording medium, an amount of correction for correcting ununiformity of the image density in the direction in which the light emission points are arranged (i.e., in the main scanning direction) is set by the amount-of-correction setting means. Based on the amount of correction, the light emission intensities of the plural light emission points are each corrected by the correction means in the direction in which the light emission points are arranged.
As a result, in the same manner as in the third aspect of the present invention, the light beam is irradiated on the image retaining member while output intensities of the light emission points are being corrected based on the density of a formed image. Accordingly, any density unevenness caused by, not only ununiformity in the amount of light, but also ununiformity of charging caused in the image retaining member, variations in the density of toner, variations in the distance, ununiform charging caused in the transfer material, variations in the nipping force, and the like can be eliminated (reduced).
According to a ninth aspect of the present invention, preferably, intensity control means for automatically controlling each of light emission intensities of the plural light emission points at a predetermined intensity level, and intensity level changing means which, when setting of the amount of correction by the amount-of-correction setting means is changed, changes the intensity level so that one of the light emission intensity in the predetermined portion of the image region, and an average value of the light emission intensities in the direction in which the light emission points are arranged becomes substantially equal before and after the setting is changed, are further provided.
That is, the light emission intensities of the light emission points are each automatically controlled at a predetermined intensity level by the intensity control means. In image forming apparatuses, generally, such automatic control for the light emission intensities is carried out based on variations measured at the time of manufacturing so as to allow correction for manufacturing variations in the light emission intensity between the light emission points. When the amount of correction set by the amount-of-correction setting means is changed (including a case in which a state of making no correction is changed to a state of making a correction), the intensity level is changed by the intensity level control means so that the light emission intensity in a predetermined portion of the image region, or an average value of light emission intensities in the direction in which the light emission points are arranged, becomes substantially equal before and after the amount of correction is changed. As a result, variations in the density of an image in the vicinity of, for example, a central portion having the highest visibility are prevented. As a result, in the same manner as in the fourth aspect, any density unevenness caused by, not only uniformity in the amount of light of the array light source, but also other factors is eliminated (reduced), and when a color image is formed, ununiform color tone caused by relative density differences between colors can be prevented.
In the above-described sixth to ninth aspects of the present invention, according to a tenth aspect of the present invention, preferably, amount-of-correction changing means is provided which makes a determination as to whether the intensity level changed by the intensity level changing means is within the predetermined range, and when it is determined that the changed intensity level exceeds the predetermined range, the amount-of-correction changing means changes the amount of correction so that the intensity level is held within the predetermined range. Further, according to an eleventh aspect of the present invention, preferably, alarm signal output means is provided which makes a determination as to whether the intensity level changed by the intensity level changing means is within the predetermined range, and when it is determined that the changed intensity level exceeds the predetermined range, the alarm signal output means outputs an alarm signal.
Moreover, according to a twelfth aspect of the present invention, preferably, pattern input means for inputting information which indicates a correction pattern of the image density, is provided, and the amount-of-correction setting means determines the amount of correction based on the information inputted from the pattern input means. At this time, in a thirteenth aspect of the present invention, preferably, level input means for inputting information which indicates a correction level of the image density, is provided, and the amount-of-correction setting means determines the amount of correction based on the information inputted from the level input means.
Still further, according to a fourteenth aspect of the present invention, preferably, detecting means for automatically detecting the density of an image on one of the image retaining member and the image recording medium, is provided, and the amount-of-correction setting means determines the amount of correction based on a result of detection by the detecting means.